1. Field of the Invention
The present invention relates generally to an imaging apparatus, and more particularly, to a media picking mechanism in an imaging apparatus.
2. Description of the Related Art
An imaging apparatus, such as a printer, scanner, or copier, includes a media picking mechanism that is used to successively pick a single sheet of media, e.g., paper from a media stack.
FIG. 1 is a perspective view of a media picking mechanism 10 according to a prior art system. The media picking mechanism 10 includes a drive shaft 12, a transmission shaft 14, and a pick shaft 16. A pivot gear 18 is mounted on the drive shaft 12. A first bevel gear 20a and a second bevel gear 20b are mounted on each end of the transmission shaft 14. The first bevel gear 20a is rotatably engaged with the pivot gear 18.
A pick gear 22 is mounted on the pick shaft 16. The pick gear 22 is rotatably engaged with the second bevel gear 20b. A first pick tire 24a and a second pick tire 24b are attached to each end of the pick shaft 16.
The media picking mechanism 10 also includes a housing 26 that contains the pivot gear 18, the first bevel gear 20a, the second bevel gear 20b, the transmission shaft 14, and the pick gear 22.
During a media picking operation, the drive shaft 12 rotates in a first direction as illustrated by the arrow 28 to provide input torque to the transmission shaft 14. The input torque rotates the transmission shaft 14 in a second direction as illustrated by the arrow 30. The transmission shaft 14 transmits the input torque to the pick shaft 16 that rotates in a third direction as illustrated by the arrow 32.
FIG. 2 is a partial perspective view of the media picking mechanism 10 illustrating forces being applied during a media picking operation. The transmission shaft 14 rotating in the second direction as illustrated by the arrow 30 applies a downward normal force Fg on the pick gear 22. The vertical component of downward force Fg is approximately equal to the sum of a first normal force FN1 and a second normal force FN2 shown at pick tires 24a, 24b, respectively.
As shown, force Fg applies a moment Mh on the housing 26 causing the portion of the housing 26 adjacent the second bevel gear 20b to twist in a direction of arrow 30. The moment Mh also causes the downward normal force FN1 applied to the first pick tire 24a towards the media 34 to be greater than the downward normal force FN2 applied to the second pick tire 24b towards the media 34. The uneven forces FN1 and FN2 applied on the media 34 causes the media 34 to skew during the media picking operation, and premature wear of the first pick tire 24a. 
Additionally, another drawback of the prior art media picking mechanism 10 is that the diameter of the pivot gear 18 increases the height of the media picking mechanism 10. The desired architecture of the media picking mechanism 10 requires that the overall height of the media picking mechanism 10 be minimized. The limiting factor for keeping the height of the media picking mechanism 10 to a minimum is the diameter of the pivot gear 18, i.e., pivot gear 18 of a smaller diameter is desired to keep the height of the media picking mechanism 10 to a minimum. However, a reduced diameter of the pivot gear 18 that is too small have been found to cause the pivot gear 18 to either break or to skip teeth when transmitting the input torque to the first bevel gear 20a during a media picking operation.
Therefore, it would be advantageous to have a media picking mechanism that provides substantially equal normal forces FN1 and FN2 to the pick tires 24a and 24b, has a near zero moment on the housing 26, and also addresses the load carrying limitation of the pivot gear 18.